Paper is a film composed of a network of welded individual fibres. Generally speaking, its production entails a wet process involving cellulose fibres. The pulp is produced from wood and the composition varies depending on the grades of paper. The sheet is formed after draining a uniform deposit on a wire provided for this purpose. The long fibres (obtained from hardwood) allow the formation of a network in which are deposited the short fibres (obtained from softwood) and the combination contributes to the mechanical strength of the material formed after drying. Additives and loadings are very often employed to improve the characteristics such as appearance, porosity and surface condition.
Beet pulps are a by-product of the sugar beet processing industry. The beets are crushed and the sugar extracted with water. This operation is followed by pressing in order to increase the dry matter content to about 25 to 30%. The main components of beet pulps are, on average, cellulose (27%), hemicellulose (29%), pectin (29%), the minor components being sugar (3%), lignin (3%) and ash (4%). These components together form the characteristic cellular structure of beet pulps. This structure consists of parenchymal cells held together and bound crosswise by xylem and tubular phloem.
Few new economic methods of exploiting beet pulps have been developed, mainly because of the rapid degradation of this material. At present, the main use consists in drying the pulps, mixing them optionally with molasses and selling them as cattle feed (70% of European pulps in 1992).
Due to the high energy costs of drying, several attempts have been made to develop new uses and new treatments for undried beet pulps. The following conversions and uses have been studied: chemical or enzyme hydrolysis, production of ethanol, biogas, enzymes, and protein-rich cattle feed. As regards the possibility of using beet pulps in fields other than those mentioned above, the production of paper seems promising. The paper industry has to face considerable pressure from the environment to improve its yield, reduce pollution, use fewer chemicals and increase recycling. The combination of these factors is not an objective that can be reached directly, and new processes and additives are constantly being developed. Until now, the use of fresh or fermented beet pulps has not been achieved. The main reasons are the small proportion of cellulose contained in the pulps and the cell structure which does not make it possible to obtain long fibres that could, for example, replace wood fibres. Consequently, beet pulps are not regarded as suitable for the production of paper as a simple wood substitute.
However, the use of dried beet pulps for the production of paper is well known. Some authors have even described the possibility of using overpressed and ultrapressed beet pulps in the production of paper (G. VACCARI et al., XX General Assembly of CITS, Munich, Jun. 26-30, 1995).
Some work has been done to obtain a material suitable for the production of paper from beet pulps. When it is used as a charge, the product originating from pulps is always the result of an extraction process.
The patent EP 0102 829 teaches a method for the separation of polymers from vegetable matter containing parenchymal cells under extreme pH conditions and at high temperature for a short reaction period. The cellulose material isolated, known as PCC (Parenchymal Cell Cellulose) is cited as being useful in food and possibly paper-making applications. But the process, which comprises a harsh chemical treatment followed by steam cracking and a separation/purification step, is complex and requires treatment of the effluent because of the chemicals used.
The patent CS 0174 308 describes a method for the production of paper from arabinose extraction residues of beet pulps.
The patent EP 0139 658 divulges a method for the depectinisation and dehydration of raw beet pulps. The raw pulps impregnated with acidified water undergo an alternating succession of compression and decompression steps. The mechanical work produces a kind of steeping of the pulp fibres. The fibres separate from one another, their directional arrangement disappears and the pectins are dissolved. The final dried product is suitable for paper production.
A single industrial process using beet pulps for the production of paper without any prior extraction has been described.
The patent EP 0644 293 reveals a process for grinding dried pulps and the use of said ground pulps as a paper charge. The dried pulps are ground and micronised. The resulting product is tested and used in the production of paper on an industrial scale. The characteristics of the paper obtained are comparable with those of the paper produced according to the same process but without beet pulps. In this process, the pulps are dried and the final charge product is not, therefore, commercially competitive compared with the other by-products such as sawdust or straw. Since the production of paper is a wet process, it does not seem useful to dry the charge which must then be rewetted afterwards. Moreover, the grinding of the dried pulps destroys the xylem and phloem which, without that, could help to increase the strength of the paper due to their fibrous structure.
The present invention relates to the use of fermented beet pulps in the production of paper. More particularly, this invention relates to a method of preparing a product derived from sugar beet pulps which may be added to the paper pulp in order to reduce the need for raw materials traditionally used in the production of paper.